1. Field of the Invention
The invention relates to the art of oil well drilling and to well drilling equipment particularly to well tubing handling apparatus preferably used in well servicing.
2. Description of the Prior Art
In oil recovery practice well servicing is a routine procedure comprising handling well elements, such as pipe, tubing and rods, going into and coming out of a well.
In handling well elements use is made of a mobile apparatus generally comprising hoisting means, gripping and rotating means for screwing and unscrewing the joints on a string of drill tubes or rods. Since well servicing is conducted on an operating well, efficiency is not least important. Well servicing time in repairs also includes the time for raising and lowering tubing strings and in all instances it is desirable to reduce this time to the minimum. The quest for time reduction in performing the above operations has led to the development of apparatus wherein all or most of the operations are automated.
The hoisting means in such apparatus generally comprises a mast arranged by the well bore and a hoisting drive usually including a rope-and-pulley system mounted on the mast. To suspend the string of drill tubes or rods use generally is made of a corresponding upper means, such as elevators and a lower means, such as spiders, one or several lifting frames being suspended from the pulley block of the hoisting drive.
Well servicing equipment also includes a means for storing drill tubes or rods usually in the form of racks located near the well bore and a means for transferring well tubes or rods from the racks to the well bore incorporating a manipulator.
To screw and unscrew the joints of a well string the apparatus comprises suitable arrangements variously constructed as well as disposed.
Known in the art is an apparatus for handling well elements disclosed in French Pat. No. 1,258,673 and comprising a swivel head to screw and unscrew the joints of a well string, the swivel head including driven and pressure rollers mounted at the end of a boom pivoted to the platform for orienting the well tube, following its transfer by the manipulator from the storage racks to the mast, into alignment with the well bore.
Another prior art apparatus of the kind disclosed (Inventor's Certificate of the USSR No. 574,517) comprises an automatic rotary tong assembly and a swivel head both mounted above the spider and by the side of a well bore.
One more prior art apparatus as disclosed in Inventor's Certificate of the USSR No. 236,377 comprises an automatic rotary tong assembly which is a self-gripping and double-acting swivel head mounted directly on the spider (rod adapter) and in alignment with the well bore.
In all the apparatus mentioned above the screwing and unscrewing operation is characterized by a low efficiency.
As regards the above-mentioned French patent a well tube is actually centered in the swivel head and aligned with the well string held in the gripping means of the drill platform but this alignment is achieved by rotating the boom of the swivel head thus consuming time and this rotation does not coincide with either raising and lowering operations or rotation of the manipulator. Moreover the above apparatus is designed for use with tubes only and cannot be used with well rods.
In the apparatus according to the Soviet Inventor's Certificate No. 574,517 both applying of the tongs on the well string and accurate alignment of the well elements making up the well string, performed by hand, require additional time.
In the apparatus according to the Soviet Inventor's Certificate No. 236,377 the tongs are substantially aligned with the well bore to exclude extra time for their application and make for convenience in unscrewing the well string. However lack of rigid guiding means for a tube or rod in screwing the well string makes it difficult for the tube or rod to pass the tongs opening and the speed of lowering the same tube or rod is to be reduced.
Also, in this apparatus a tube or rod is to be lowered or raised half the vertical travel distance with the height of the tongs inclusive in screwing and unscrewing the well string, respectively so that time consumed for travelling the distance equal to the height of the tongs is to be added to that required for the reduction in the tube lowering speed.